1. Field of the Invention
The present invention relates to an automatic exposure control apparatus for a camera which meters a reflected light from a film surface in a flash photographing mode and stops light emission in accordance with the metering.
2. Related Background Art
A camera which detects a reflected light from a film surface after a shutter has been opened in a steady state light photographing mode to meter a light intensity and which closes the shutter when the metering output reaches a predetermined level has been known. Further, a camera which emits a flashing light by an electronic flashing device after the shutter has been opened, detects a reflected light from the film surface to meter a light intensity, and stops the light emission when the metering output reaches a predetermined level has also been known.
A reflective index of the film surface varies from film to film and the metering output for the reflected light varies with the reflective index. Thus, if the closure of the shutter or the termination of the light emission is controlled under the same condition without taking the reflective index of the film into account, under-exposure or over-exposure may result in depending on the film. Japanese Laid-Open Patent Application No. 57-4027 discloses a camera which intends to avoid such a problem. In the reference, a metering output (first metering output) in a shutter closure state and a metering output in a shutter partially open state (second metering output) are compared to determine a difference therebetween (which depends on a difference between reflective indices of a shutter curtain surface and a film surface), and a timing to close the shutter is determined while such a difference is taken into account. In this method, proper exposure is always attained in the steady state light photographing mode without regard to variation in the reflective index of the film plane.
Such a prior art method is effective in determining the timing to close the shutter in the steady state light photographing mode, but it is not proper in determining a timing to stop the light emission in the flash photographing mode. In the steady state light, the light intensity can be deemed as essentially constant with time as shown in FIG. 1A and the first metering output and the second metering output can be obtained under the same condition. By contrast, the light intensity in the flash light emission varies with time as shown in FIG. 1B. As will be appreciated from FIG. 1B, even if a first metering output and a second metering output are both obtained during the flash they cannot be compared under the same condition, and the difference between the reflective indices of the film surface and the shutter curtain surface cannot be determined.